Sodium-potassium ionic ratio correlates with yeast induction from Mucor circinelloides Tieghem

A critical feature of fungal dimorphism is the morphogenetic conversion from mold to the yeast form. In the conversion of a fungus to the yeast form, little is known about the morphological changes that occur prior to the latter. A previous study from our laboratory showed that K+ plays important role in the generation of protoplasts from sporangiospores; other morphologies exhibited included thallo-arthric-, holothallic-, holoblastic conidia as well as septate hyphae with provenant vesicular chains of conidia and yeast cells but phenotypic variabilithy of stable forms also exhibited in synthetic broth in a study conducted at pH 4.5 and temperature 20°C. This was confirmed in this study. We further show that phenotypic modification resulting in several transient forms occurred during the early growth phase that led to conversion of germ cell to neoplast, then through protoplast to prevegetative cell and nascent yeast. On modulating K+ concentrations with Na+, growth pattern exhibited was either biphasic or sigmoid, which was at optimal at yeast induction sigmoid curve and its phases correlated with dynamic changes in ionic flux, with a Na+/K+ ratio of 0.78 at lag- and 2.90 at exponential phase. It was thought that in the pH - profile two-phase anisotropic growth environment, transmembrane proton ion gradient favoured ionic circulation that triggered phenotypic modification in which protoplasts were generated and, subsequently, prevegetative cells evolved from simultaneous with metabolic adjustment. Subsequently, cells became vegetative in the yeast form. Our data suggest that diminishing logarithmic growth in the sigmoid pattern was triggered by rapid Na+ extrusion from intracellular medium of the induced yeast.   Key words: Sporangiospore, synthetic broth, yeast cells, proton gradient, Na+/K+ ratio.